Adhesive composition for bonding different members, bonding method using the composition and composite members bonded by the bonding method

ABSTRACT

An adhesive composition is provided for bonding two or more different members which can give a bonded material having excellent heat resistance characteristics while inhibiting breakage of the materials to be bonded by reducing the expansion coefficient, the Young&#39;s modulus and the proof stress value. A method for bonding two or more different members using the adhesive composition, and a composite member comprising two or more different members bonded by the above method can be provided by the adhesive composition which comprises a hard solder and a mixture of at least two fine particle materials differing in wettability with the hard solder and which is controlled in expansion coefficient, Young&#39;s modulus and proof stress value.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is division of U.S. application Ser. No.10/178,624, filed Jun. 24, 2002, which in turn is a division of U.S.application Ser. No. 09/689,129, filed Oct. 12, 2000, now U.S. Pat. No.6,440,578, the entireties of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to an adhesive composition forbonding two or more different members through a fitting structure, abonding method using the composition, and a composite member made by thebonding method. More particularly, it relates to an adhesive compositionfor making a composite member comprising two or more different membersbonded through a fitting structure which is controlled in its expansioncoefficient and residual stress, a method for bonding two or moredifferent members using the composition, and a composite member made bythe bonding method.

[0003] There is a method of using a solder for bonding differentmembers, for example, a ceramic member and a metallic member. However,during cooling operation after bonding them at high temperatures,thermal stress is generated due to the difference in thermal expansioncoefficients between the different members or between the member and thesolder used for bonding of these different members to cause separationat the bonded interface. If one of the members is fragile, cracks occurin the vicinity of the bonded interface and sometimes the desiredbonding strength or airtightness cannot be obtained. The products inwhich these defects are caused during the production steps must bedisposed of as rejected products, and this results in an increase of theproduction cost for these composite members. Moreover, if they aresubjected to thermal cycles in use, the defects occur after use for acertain period to cause deterioration of reliability of the products.

[0004] When different members are bonded using a solder, a method isgenerally employed according to which the surface of the ceramic memberto be bonded is plated with a metal such as Ni to ensure wetting betweenthe ceramic member and the solder. Then these members are disposedopposite to each other with a suitable space, the solder is poured intothe space, and the members are bonded. There is another method accordingto which an additive such as Ti, which can ensure wetting by forming areactive layer of a nitride or an oxide on the surface of the ceramicmember, is added to the solder, without carrying out the plating with ametal. However, these methods are not preferred because they are notenough to reduce the thermal stress, and cracks are often formed on theside of the ceramic member which is fragile against thermal stress orseparation is caused at the bonded part to adversely affect variousperformances such as bonding strength and airtightness required forcomposite member.

[0005] As methods for relaxing the thermal stress, a method of using ametal low in thermal expansion coefficient as an intermediate materialat the time of bonding and a method of using as an intermediate materiala soft metal which is high in reactivity with ceramics and can relax thestress by plastic deformation are generally employed. However, thesetechniques also suffer from the problems caused by difference in thermalexpansion between the solder and the member, for example, low thermalcycle characteristics, and cannot necessarily be said to be high ingeneral-purpose properties. Furthermore, there is a high-pressure solidphase bonding method which is now under development, but this method hasunsolved problems for practical utilization and cannot provide asufficient bonding strength.

[0006] On the other hand, as a composite solder, JP-A-6-126479 disclosesa mixture of powders comprising materials having a higher melting pointthan the solder used for bonding a semiconductor chip and a substrate.However, this aims to solve the problem of insufficient wetting of theconventional composite solder caused by the powder also present on thesurface by filling a powder comprising materials higher in melting pointthan the solder only in the central portion of the solder per se. Inother words, this aims to increase the bonding strength at the bondedinterface. This composite solder is not effective for decreasing thermalstress, and, hence, is not effective in solving the problems caused bythe thermal stress between the members to be bonded or between themember and the solder.

[0007] As a result of intensive research conducted by the inventors forattaining the above object, they have found an adhesive composition forbonding at least two different members which does not cause decrease ofbonding strength in the vicinity of the bonded interface due to thermalstress generated during cooling operation after bonding at hightemperatures and does not cause generation of cracks in the member weakagainst the thermal stress during the cooling operation whilemaintaining an appropriate bonding strength between the differentmembers. A Japanese Patent Application No. 10-52971 was filed on thissubject.

[0008] That is, as a result of intensive research, the inventors havefound that at least two different members can be bonded without causinga decrease in the bonding strength in the vicinity of the bondedinterface due to thermal stress generated during cooling operation afterbonding at high temperatures and without causing generation of cracks inthe member weak against the thermal stress during the cooling operationwith maintaining an appropriate bonding strength between the differentmembers by using as a base a hard solder which is not restricted by thekind of the members or shape of the members and which leaves room forselection of bonding shape and by adding to the hard solder a fineparticle material which lowers the thermal stress. Thus, the abovepatent application was filed.

[0009] As a method for bonding with the above composition, the patentapplication discloses a method which comprises disposing two or moredifferent members differing in thermal stress so that they are opposedwith a space enough to bond them, and pouring the composition into thespace or filling a given amount of ceramic or cermet fine particles andsubsequently pouring a given amount of the hard solder in molten state,followed by cooling to produce a composite member. However, thecomposition cannot be used as it is for bonding the members without asufficient space provided therebetween to be able to pour a given amountof the hard solder.

[0010] In the case of bonding two or more different members which mustbe bonded through a fitting structure, especially, in the case ofbonding the members with selecting a very narrow clearance of about0.01-0.30 mm, various troubles often occur unless a solder is filledalso on the side of the members as uniformly as possible. On the otherhand, when the clearance is greater than the above upper limit, crackssometimes occur due to the residual stress which is generated due tonon-uniform filling of the solder in the clearance and is contained inthe solder at the time of melting of the solder. This will be morespecifically explained.

[0011] For example, when a member having a columnar dented portion and amember having a columnar protruded portion are fitted, if the solder tobe uniformly filled in the columnar clearance formed by these members isone-sidedly filled on only one side because the clearance has a room tosome extent, the balance of thermal shrinkage stress is lost in theprocess of cooling and solidifying the solder and the member having thecolumnar protruded portion is pulled to one direction, resulting inresidual stress and cracks. Moreover, there are demands for dimensionalaccuracy and beautiful appearance of the composite member as a finishedproduct. Thus, since it is substantially impossible to pour a givenamount of a hard solder from a narrow clearance in the members havingonly such a narrow clearance, these different members cannot be bondedby the above method. The term “clearance” here means a width of thespace present between the wall surfaces of the different members in thefitting structure.

[0012] Under the circumstances, in an attempt to solve these problems,the inventors have found that a member having a dented portion whichforms a fitting structure and a member having a protruded portion whichforms a fitting structure and being different from the member having thedented portion can be bonded by fitting them to each other in thefollowing manner.

[0013] A fine particle material is uniformly spread over the surface ofthe dented portion of the member having the dented portion, then a platyor powdery hard solder is disposed so as to cover at least a part of thelayer comprising the fine particle material, further the member havingthe protruded portion is disposed, these are heated to a giventemperature under application of pressure to melt the hard solder. Thismolten hard solder is penetrated into the layer comprising the fineparticle material to form a bonding layer of an adhesive compositioncontrolled in expansion coefficient and comprising the hard solder andthe fine particle material, or a fine particle material is uniformlyspread over the surface of the dented portion of the member having thedented portion. Then the member having the protruded portion having oneor a plurality of holes in which a hard solder is inserted is disposedso as to closely contact with the layer comprising the fine particlematerial. These are heated to a given temperature under application ofpressure to melt the hard solder, and this molten hard solder ispenetrated into the layer comprising the fine particle material to forma bonding layer of an adhesive composition controlled in expansioncoefficient and comprising the hard solder and the fine particlematerial.

[0014] An alternative is a member having a protruded portion at the endof which is formed a layer comprising a hard solder and a fine particlematerial is previously prepared, only a hard solder is disposed on thesurface of a dented portion of a member having the dented portion, themember having the protruded portion at the end of which is formed alayer comprising the hard solder and the fine particle material isdisposed on the hard solder disposed on the surface of the dentedportion of the member, these are heated to a given temperature underapplication of pressure to melt the layer comprising the hard solder andthe particulate material formed at the end of the member having theprotruded portion and the hard solder disposed on the surface of thedented portion of the member having the dented portion, thereby to forma bonding layer of an adhesive composition controlled in expansioncoefficient and comprising the hard solder and the fine particlematerial. Based on this finding, Japanese Patent Application No.11-180902 was filed on Jun. 25, 1999.

[0015] Furthermore, the Japanese Patent Application No. 11-180902 filedon Jun. 25, 1999 proposes a composite member having improved thermalcycle characteristics and comprising two or more different membersobtained by the above fitting and bonding method, characterized bycomprising at least a member having a dented portion which forms afitting structure and a member having a protruded portion which forms afitting structure and being different from the member having the dentedportion, said different members being fitted and bonded to each otherwith an adhesive composition controlled in expansion coefficient andcomprising a fine particle material and a hard solder.

[0016] However, the dispersing material dispersed in the hard solder issubjected to plating with Ni in order to ensure wetting with the hardsolder. The solder layer, which is a composite formed by this method,has a lower expansion coefficient than the hard solder, which is ametallic material, and is effective in inhibiting breakage of theceramic, which is a material to be bonded, and in improving the thermalcycle characteristics of the bonded part. But when strength of theceramic (which is the material to be bonded) is low, for example, in thecase of aluminum nitride or the like, it is difficult to completelyinhibit the breakage. And with increase of the area of the bonded part,the possibility of the occurrence of breakage further increases, and,besides, there is a problem that if the number of the bonded parts inone product is great, the percent defective of the products cannot beignored. For the inhibition of breakage of the materials to be bonded,in addition to reduction of expansion coefficient of the solder,reduction of Young's modulus and reduction of proof stress value areeffective, but it has been found that positively advantageous operationfor all of these physical characteristics is difficult using only thesemethods.

SUMMARY OF THE INVENTION

[0017] The object of the present invention is to provide an adhesivecomposition for bonding two or more different members which can give abonded material excellent in heat resistance and other characteristicswhich inhibit breakage of the materials to be bonded by controlling thecharacteristics of the above-mentioned composite solder, namely,reducing the expansion coefficient, reducing the Young's modulus and theproof stress value. A method for bonding two or more different membersusing the adhesive composition, and a composite member comprising two ormore different members bonded by the above method is also provided.

[0018] As a result of intensive research conducted by the inventors forattaining the above object, it has been found that the above object canbe attained by an adhesive composition for bonding two or more differentmembers which comprises a hard solder and a mixture of two or more fineparticle materials differing in wettability with the hard solder. As aresult, the present invention has been accomplished.

[0019] Moreover, it has been found that a bonded material of a compositemember comprising different members bonded through a fitting structurewhich is inhibited from breaking and excellent in heat resistancecharacteristics and others can be produced by using an adhesivecomposition controlled in expansion coefficient, Young's modulus andproof stress value by the above-mentioned method. Thus, the presentinvention of the second aspect has been accomplished.

[0020] Furthermore, it has been found that a composite member excellentin heat resistance characteristic and others which comprises a memberhaving a dented portion which forms a fitting structure and a memberhaving a protruded portion which forms a fitting structure and beingdifferent from the member having the dented portion, the differentmembers being fitted and bonded to each other with a bonding layercomprising a hard solder and a mixture of two or more fine particlematerials differing in wettability with the hard solder, can be obtainedwithout causing breakage by using the adhesive composition controlled inexpansion coefficient, Young's modulus and proof stress value. Thus, thepresent invention of the third aspect has been accomplished.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is an optical microphotograph which shows themicrostructure of an adhesive prepared using only the fine particlematerial subjected to plating treatment.

[0022]FIG. 2 is an optical microphotograph which shows themicrostructure of an adhesive prepared using the fine particle materialsubjected to no plating treatment and the fine particle materialsubjected to plating treatment at a ratio of 1:3.

[0023]FIG. 3 is an optical microphotograph which shows themicrostructure of an adhesive prepared using the fine particle materialsubjected to no plating treatment and the fine particle materialsubjected to plating treatment at a ratio of 1:2.

[0024]FIG. 4 is an optical microphotograph which shows themicrostructure of an adhesive prepared using the fine particle materialsubjected to no plating treatment and the fine particle materialsubjected to plating treatment at a ratio of 1:1.

[0025]FIG. 5 is a cross-sectional view of a bonded structure formedaccording to one embodiment of the present invention.

[0026]FIG. 6 is a cross-sectional view of a bonded structure formedaccording to another embodiment of the present invention.

DESCRIPTION OF THE INVENTION

[0027] The first aspect of the present invention relates to an adhesivecomposition for bonding two or more different members which comprises ahard solder and a mixture of two or more fine particle materialsdiffering in wettability with the hard solder. In this adhesivecomposition, the base metal constituting the hard solder is Au, Ag, Cu,Pd, Al or Ni, and the mixture of two or more fine particle materialsdiffering in wettability with the hard solder is preferably a mixture ofceramic fine particles, cermet fine particles or low-expansion metalfine particles which are not surface treated and ceramic fine particles,cermet fine particles or low-expansion metal fine particles which aresurface treated. In the mixture of two or more fine particle materialsdiffering in wettability with the hard solder, the mixing ratio of thefine particle material which is not surface treated and the fineparticle material which is surface treated is preferably 5:95-80:20. Theterm “materials differing in wettability with the hard solder” means acombination of a material superior in relative wettability with the hardsolder and a material inferior in relative wettability with the hardsolder.

[0028] Examples of the combination of a material superior in relativewettability with the hard solder and a material inferior in relativewettability with the hard solder are a combination of ceramic fineparticles subjected to surface treatment such as plating and ceramicfine particles subjected to no surface treatment, a combination oflow-expansion metal fine particles subjected to surface treatment suchas plating or subjected to no surface treatment and ceramic fineparticles subjected to no surface treatment, and other combinations. Theplating method here is not limited, but electroless plating is suitable.

[0029] Furthermore, without carrying out the metal plating treatment,wettability with the hard solder can be ensured by incorporatingadditives, such as Ti in the form of fine particles, into the solder, orby adding the fine particle material to form a reactive layer of activematerials such as a nitride, an oxide, a carbide and the like on thesurface of the ceramic. In this case, if those differing in wettabilitywith the hard solder containing the additive are combined, theabove-mentioned effect can be exhibited. For example, when thecombination of the dispersing materials is nitride and oxide or nitrideand carbide, the effect can be satisfactorily exhibited. The amount ofthe active materials is suitably about 0.5-5% in weight ratio based onthe amount of hard solder.

[0030] That is, the fine particle materials comprising two or morematerials differing in wettability with the hard solder can be easilyprepared, for example, by mixing alumina particles of a desired particlesize, (for example, alumina particles 50 μm in average particlediameter) which are subjected to Ni plating of about 0.5 μm as theparticles subjected to surface treatment in a desired thickness withalumina particles of a desired particle size, (for example, 50 μm inaverage particle diameter) as the particles subjected to no surfacetreatment. The fine particle materials comprising two or more materialsdiffering in wettability with the hard solder containing a given amountof Ti or the like as the additive can be easily prepared by mixingaluminum nitride of a desired particle size, (for example, 50 μm inaverage particle diameter) with alumina particles of a desired particlesize, (for example, 50 μm in average particle diameter).

[0031] The mixing ratio of the fine particle material subjected to nosurface treatment to the fine particle material subjected to surfacetreatment is more preferably in a range of 1:9, (namely, the fineparticle material subjected to no surface treatment occupies about 10%of all particles), to 3:1, (namely, the fine particle material subjectedto no surface treatment occupies about 75% of all particles). Furtherpreferably, the mixing ratio is in a range of about 1:3-1:1.

[0032] If the mixing ratio of the material subjected to no surfacetreatment is increased to more than 3:1, the action and effect as anadhesive is considerably lowered, and this is not preferred. Inobtaining the adhesive composition of the present invention, the hardsolder to be penetrated and the penetration method and conditions can bein accordance with the disclosure of Japanese Patent Application No.11-180902. Moreover, the fine particle material subjected to the surfacetreatment for ensuring the wettability and the fine particle materialsubjected to no surface treatment can be the same materials, as long asthe fine particle material subjected to the surface treatment forensuring the wettability and the fine particle material subjected to nosurface treatment for ensuring the wettability are combined. In otherwords, it is a matter of course that the same materials different inonly whether they are subjected to or not subjected to the platingtreatment may be used.

[0033] The hard solders used for the adhesive compositions in thepresent invention include, for example, solders containing as a base ametal such as Au, Ag, Cu, Pd, Al or Ni. Of course, those which are moresuitable can be used depending on wettability between the members to bebonded and the solders, reactivity between the members to be bonded ordispersion particles and the solders, or temperature conditions of usingthe solders. In the case of bonded members being used at anenvironmental temperature of 500° C. or lower, Al-based solders such asBA4004 (Al-10Si-1.5 Mg) may be suitably used. In the case of the bondedmembers being used at an environmental temperature of 500° C. or higher,Au, BAu-4(Au-18Ni), BAg-8(Ag-28Cu) and the like may be suitably used.

[0034] By using the adhesive composition of the present invention, abonded material having excellent heat resistance characteristics andothers while inhibiting breakage of the materials to be bonded can beobtained by positively partly reducing the interface bonding forcebetween the hard solder and the dispersing material dispersed in thehard solder, or by positively forming fine voids in the adhesivecomposition, to thereby reduce the Young's modulus and proof stressvalue in addition to reducing the expansion coefficient. Morespecifically, this effect can be attained by using a mixture ofparticles having superior wettability with respect to the hard solderand particles inferior in wettability with the hard solder as a materialto be dispersed in the hard solder. As suitable combinations of theparticles superior in wettability with the hard solder and the particlesinferior in wettability with the hard solder, combinations of particlessubjected to the surface treatment such as plating for ensuringwettability with the hard solder and the particles subjected to no suchsurface treatment may be used, such as a nitride and an oxide,low-expansion metal particles and an oxide, and the like.

[0035] When the proportion of the particles superior in wettability withthe hard solder is great, the optically observed microstructure of theadhesive composition does not substantially differ from that of theadhesive composition prepared using only the particles subjected to thesurface treatment. While the reduction of the expansion coefficient andthe reduction of Young's modulus is equal to those of the adhesivecomposition prepared using only the particles superior in wettabilityare attained, the effect of the reduction in proof stress value ishigher than that of the adhesive composition prepared using only theparticles subjected to the surface treatment. It is considered that thisis because the interfacial bonding force between the particles inferiorin wettability and the hard solder is reduced as compared with thatbetween the particles superior in wettability and the hard solder, and,as a result, the characteristics of the adhesive composition arecontrolled.

[0036] Moreover, when the proportion of the particles inferiorwettability with the hard solder is increased, optically observablevoids are formed in the adhesive composition. As a result, in additionto the reduction of expansion coefficient being equal to that of theadhesive composition prepared using only the particles superior inwettability, greater reductions of Young's modulus and proof stressvalue can be attained as compared with those of the composition having asmaller amount of the particles inferior in wettability with the hardsolder. It is understood that this is because in the composition havinga larger amount of particles inferior in wettability with the hardsolder, in addition to reducing the interfacial bonding force betweenthe dispersing material and the hard solder, the apparent sectional areaof the composition decreases due to the presence of the voids formed,and, as a result, Young's modulus is reduced. Additionally, the proofstress value is reduced because the portion near the void becomes acrack forming point upon loading.

[0037] In explanation of the mechanism to develop the effect exhibitedby the adhesive composition of the present invention, for convenience'sake, the action and the effect have been explained according to theamount of the particles subjected to no surface treatment for ensuringthe wettability such as plating treatment, but the purpose, thepreparation method, the action and the effect are the same and thenecessity to severely specify the boundary is small. However, it maybecome necessary in considering the sealability of the adhesivecomposition at the bonded portion.

[0038] In order to efficiently reduce the thermal stress, it isnecessary to adjust the kind of fine particle material and packingdensity thereof in the hard solder, and, for this purpose, it isnecessary to adjust the thermal expansion coefficient of the adhesivecomposition layer. As the fine particle materials which reduce thethermal stress, those having a smaller expansion coefficient are moreadvantageous for reducing the thermal expansion coefficient of theadhesive composition layer. The packing density of the fine particlematerial for the hard solder is 30-90%, preferably 40-70% by volume. Inthe case of dispersing the particles superior in wettability with thehard solder and the particles inferior in wettability with the hardsolder, the ratio by volume of the particles calculated on theassumption that there are no voids in the adhesive composition is also30-90%, preferably 40-70%. In these cases, increasing the packingdensity of the fine particle material is advantageous for reducing theexpansion coefficient, but too high packing density is not preferredbecause deterioration of bonding strength is sometimes caused. If thepacking density is lower, sometimes the desired expansion coefficientcannot be obtained, and care should be taken in this respect. That is,adjustment of the expansion coefficient can be attained by selecting thekind of the fine particle material so as to be able to attain thedesired expansion coefficient or by suitably selecting the particle sizedistribution of the fine particle material.

[0039] The second aspect of the present invention relates to a methodfor producing a composite member comprising different members by fittingand bonding a member having a dented portion which forms a fittingstructure and a member having a protruded portion which forms a fittingstructure and being different from the member having the dented portion.The method includes the following steps: a step of uniformly spreading amixture of at least two fine particle materials differing in wettabilitywith the hard solder over the surface of the dented portion of themember having the dented portion, then disposing a platy or powdery hardsolder so as to cover at least a part of the layer comprising themixture of at least two fine particle materials differing in wettabilitywith the hard solder, and further disposing the member having theprotruded portion. Alternatively, the method includes a step ofuniformly spreading a mixture of at least two fine particle materialsdiffering in wettability with a hard solder over the surface of thedented portion of the member having the dented portion and disposing themember having the protruded portion having one or a plurality of holesin which a hard solder is inserted so as to closely contact with thelayer comprising the fine particle materials; or previously preparing amember having a protruded portion at the end of which is formed a layercomprising a hard solder and a mixture of at least two fine particlematerials differing in wettability with the hard solder, disposing ahard solder on the surface of a dented portion of a member having thedented portion and disposing thereon the member having the protrudedportion having the layer, and a step of heating them to a giventemperature under application of pressure to melt the hard solder andimpregnating the mixture of at least two fine particle materialsdiffering in wettability with the hard solder with said molten hardsolder to form a bonding layer comprising the hard solder and the fineparticle materials, thereby to bond the different members through thefitting structure.

[0040] The first embodiment of the bonding method according to thesecond aspect of the present invention, shown in FIG. 5, is a method forbonding different members through a fitting structure which comprisesuniformly spreading a mixture (4) of at least two fine particlematerials differing in wettability with the hard solder over the surfaceof a dented portion of a member (1) having the dented portion, thendisposing a platy or powdery hard solder (3) so as to cover at least apart of the layer comprising the mixture of at least two fine particlematerials differing in wettability with the hard solder, furtherdisposing a member (2) having a protruded portion, heating them to agiven temperature under application of pressure to melt the hard solderand impregnate the fine particle materials with this molten hard solderto form a bonding layer of an adhesive composition comprising the hardsolder and the fine particle materials. In this case, a mixture of thefine particle materials with the powdery hard solder may be used inplace of the layer comprising the fine particle materials and the platyor powdery hard solder which covers said layer.

[0041] The second embodiment is a method for bonding different membersthrough a fitting structure which comprises uniformly spreading amixture (4) of at least two fine particle materials differing inwettability with the hard solder over the surface of a dented portion ofa member (1) having the dented portion, disposing the member (2) havingthe protruded portion having one or a plurality of holes in which a hardsolder (3) is inserted so that the member (2) closely contacts with thelayer comprising the fine particle materials, heating them to a giventemperature under application of pressure to melt the hard solder andimpregnate the mixture of at least two fine particle materials differingin wettability with the hard solder with this molten hard solder to forma bonding layer of an adhesive composition comprising the hard solderand the fine particle materials.

[0042] The third embodiment is a method for bonding different membersthrough a fitting structure, shown in FIG. 6, which comprises previouslypreparing a member (2) having a protruded portion in the end of which isformed a hard solder (3) and a mixture (4) of at least two fine particlematerials differing in wettability with the hard solder is disposed in adented portion of a member (1), disposing thereon said member having theprotruded portion having said layer, heating them to a given temperatureunder application of pressure to melt the layer which comprises the hardsolder and the mixture of at least two fine particle materials differingin wettability with the hard solder and which is formed at the end ofthe member having the protruded portion and the hard solder which isdisposed on the surface of the dented portion of the member having thedented portion, thereby to form a bonding layer comprising the hardsolder and the fine particle materials.

[0043] Conditions employed for bonding other than those mentioned above,for example, disposing method of the materials, melting conditionsincluding melting temperature and others, cooling conditions and thelike can be in accordance with the disclosures of Japanese PatentApplication No. 10-52971 filed on Feb. 18, 1998 and Japanese PatentApplication No. 11-180902 filed on Jun. 25, 1999.

[0044] As examples of combination of the two or more different membersused in the present invention, mention may be made of combinations ofceramics members such as of aluminum nitride and silicon nitride withmetallic members such as of molybdenum, Kovar and tungsten, orcombinations of different ceramics members differing in the startingmaterials. More specific examples are composite members obtained byfitting and bonding aluminum nitride members which are used inproduction of semiconductor wafers and exhibit electrostatic chuckfunction or heater function by metal electrodes or metal electricalheating elements incorporated therein with metallic molybdenum membersbonded as terminals for supplying electricity to the incorporated metalelectrodes or the like.

[0045] As a third aspect of the present invention, a composite membercomprising at least two different members in which a member having adented portion which forms a fitting structure and a member having aprotruded portion which forms a fitting structure and being differentfrom the member having the dented portion are fitted with each other andbonded with a bonding layer of an adhesive composition comprising a hardsolder and a mixture of at least two fine particle materials differingin wettability with the hard solder, can be produced by theabove-mentioned method. A clearance formed in the fitting structureportion between the wall surface of the member having a dented portionand the wall surface of the member having a protruded portion canusually range from about 0.01-0.3 mm, preferably about 0.02-0.07 mm. Ifthe clearance is less than the above lower limit, there is thepossibility that the members cannot be fitted, and if it is more thanthe upper limit, there is the possibility that the solder is one-sidedlyfilled as mentioned above.

[0046] The present invention will be explained by the followingexamples, which never limit the present invention. Evaluation of bondingstate and thermal cycle resistance was conducted by judging whetherdeterioration of tensile strength of the bonded portion occurred afterbeing exposed to the thermal cycle atmosphere. In this case, when thestrength deteriorated at least 25% than before being exposed to thethermal cycling atmosphere, the sample was judged to be bad. Forreference, whether cracking or peeling at the bonded portion occurredwas also examined by observing a section of the bonding layer.

EXAMPLE 1

[0047] Dispersing particles comprising a mixture of alumina of 50 μm inaverage particle size, the surface of which was plated with Ni at athickness of about 0.3 μm, and alumina of 50 μm in average particle sizesubjected to no surface treatment at a mixing ratio of 1:0, 3:1, 2:1,1.5:1, 1:1 or 1:3 were impregnated with a hard solder A5005 (Al-0.8 Mg)under application of a given pressure, followed by coagulation to obtainan adhesive composition. A sample was prepared from the adhesivecomposition, and mechanical physical properties of the sample weremeasured and the results are shown in Table 1. Optical microphotographsof microstructures of the representative samples are shown in FIGS. 2-4.FIG. 1 is an optical microphotograph showing microstructure of a samplewhich was prepared by using a fine particle material comprising onlyalumina of 50 μm in average particle size subjected to Ni plating as acomparative example. TABLE 1 Mechanical physical properties of adhesivecompositions Thick- Amount of ness of plated Expansion Young'sProportional plating particles coefficient modulus limit (μm) (%) (10⁻⁶)(GPa) (MPa) Note 0.3 100 13.4 103 70 0.3 75 13.5 101 65 0.3 67 13.2 9563 0.3 60 13.1 75 52 0.3 50 13.5 57 45 0.3 25 — — — Difficulty in stablebonding

EXAMPLE 2

[0048] Dispersing particles comprising a mixture of alumina of 50 μm inaverage particle size, the surface of which was plated with Ni at athickness of about 1 μm, and alumina of 50 μm in average particle sizesubjected to no surface treatment at a mixing ratio of 1:0, 3:1, 2:1,1.5:1, 1:1 or 1:3 were impregnated with a hard solder A5005 (Al-0.8 Mg)under application of a given pressure, followed by coagulation to obtainan adhesive composition. A sample was prepared from the adhesivecomposition, and mechanical physical properties of the sample weremeasured and the results are shown in Table 2. TABLE 2 Mechanicalphysical porperties of adhesive compositions Thick- Amount of ness ofplated Expansion Young's Proportional plating particles coefficientmodulus limit (μm) (%) (10⁻⁶) (GPa) (MPa) Note 1.0 100 13.1 135 103 1.075 13.5 129 91 1.0 67 12.8 102 83 1.0 60 13.3 90 62 1.0 50 12.2 70 471.0 25 13.0 59 25

EXAMPLE 3

[0049] As a member having a dented portion which forms a fittingstructure, an aluminum nitride member having a thickness of 10.0 mm andhaving a vertically bored hole of 5.07 mm in diameter and 9.5 mm indepth used for fitting, and as a member having a protruded portion whichforms a fitting structure and being different from the member having adented portion, a columnar metallic molybdenum member of 5.0 mm indiameter and a length of 15.0 mm were bonded in the following manner.

[0050] As dispersing particles, a mixture comprising alumina of 50 μm inaverage particle size, the surface of which was plated with Ni at athickness of about 0.3 μm, and alumina of 50 μm in average particle sizesubjected to no surface treatment at a mixing ratio of 1:0, 2:1 or 1:1was uniformly spread over the surface of the dented portion of thealuminum nitride member plated with Ni at a thickness of about 0.5 μm.The thickness of the dispersing particle layer was 0.8 mm. A hard solderA5005 (Al-0.8 Mg) disposed so as to cover the dispersing particles wasmolten during heating and penetrated into the layer comprising the fineparticle material to form a composite bonding layer. Thus, two kinds ofsamples were prepared in which bonding was performed with a compositebonding layer comprising a hard solder and a mixture of at least twofine particle materials differing in wettability with the hard solder,and one kind of sample in which bonding was performed with a compositebonding layer comprising a hard solder and a fine particle materialcomprising only alumina of 50 μm in average particle size subjected toNi plating as a comparative example. The thickness of the compositebonding layer formed was 0.8 mm.

[0051] The resulting bonded members were subjected to a thermal cycletest. The thermal cycle test was conducted by repeating 50 times thecycle which comprised heating the bonded member from 60° C. to 180° C.at a heating rate of 2.5° C./min, immediately after reaching 180° C.,cooling the bonded member to 60° C. at a cooling rate of −2.5° C./minand immediately after reaching 60° C., repeating this cycle. The degreeof occurrence of cracks in aluminum nitride after the thermal cycle testis shown in Table 3. Moreover, the results of bond strength testsbetween the molybdenum terminal and aluminum nitride before and afterbeing subjected to the thermal cycle test are shown in Table 4. TABLE 3Inhibition effect of breakage of the bonded member Effect of inhibitionof breakage Amount of (No. of plated Expansion Young's Proportionalbroken particles coefficient modulus limit samples/No. (%) (10⁻⁶) (GPa)(MPa) of samples) 100 13.1 135 103 75 13.5 129 91 67 12.8 102 83

[0052] TABLE 4 Bond strength of bonded members Ratio of strengthStrength before and Amount of Strength after after Example or plated asthermal thermal Comparative particles Bonded cycle test cycle testExample (%) (MPa) (MPa) (%) Com. Exam. 1 100 4723 4969 103 Com. Exam. 2100 5069 4794 100 Com. Exam. 3 100 4639 4549 95 Exam. 1-1 67 4768 449094 Exam. 1-2 67 4330 4930 101 Exam. 1-3 67 4530 4750 100 Exam. 2-1 504930 4380 92 Exam. 2-2 50 4944 5120 110 Exam. 2-3 50 4730 4530 97

[0053] As is clear from the results of tests shown in the above Table 1and microphotographs of microstructures of the accompanying FIGS. 2-4,in the case of the adhesive compositions for bonding according to thepresent invention, since the bonding force between the dispersingmaterial and the hard solder is partially controlled or fine voids areintroduced into the microstructure, the portions controlled in thebonding force or the voids introduced act as breakage starting points.As a result, breakage can be effectively avoided also when forces, suchas thermal stress, are applied as shown in the above Table 3. As shownin Table 1, in the case of the adhesive compositions for bondingaccording to the present invention, the reduction of Young's modulus andthe reduction of proof stress value are recognized, but the thermalexpansion coefficient is substantially the same as the composition usingonly the fine particle material subjected to plating treatment. As aresult, there are no differences in strength of the bonded body asbonded and heat resistance of the bonded body as shown in Table 4. Thisis a noticeable point.

[0054] By using the adhesive compositions for bonding according to thepresent invention, even when the strength of the ceramic member, such asaluminum nitride, is low, a bonded body having excellent heat resistancecharacteristics and the like can be obtained while inhibiting breakageof the member to be bonded by carrying out control of thecharacteristics of the composite solder, namely, a reduction of Young'smodulus and a reduction of proof stress value in addition to a reductionof expansion coefficient. Moreover, according to the bonding methodusing the adhesive composition for bonding of the present invention,breakage which may occur in the members to be bonded or failure ofbonding can be avoided by reducing the stress remaining between themembers to be bonded, and a composite member comprising differentmembers which is high in reliability can be produced. Thus, a compositemember comprising different members which is high in reliability can beprovided.

What is claimed is:
 1. A method for producing a composite membercomprising different members by fitting and bonding a member having adented portion which forms a fitting structure and a member having aprotruded portion which forms a fitting structure and being differentfrom the member having the dented portion, said method comprising thefollowing steps: a step of uniformly spreading a mixture of at least twofine particle materials differing in wettability with a hard solder overthe surface of the dented portion of the member having the dentedportion, then disposing a platy or powdery hard solder so as to cover atleast a part of the layer comprising the fine particle materials, andfurther disposing the member having the protruded portion; or uniformlyspreading a mixture of at least two fine particle materials differing inwettability with a hard solder over the surface of the dented portion ofthe member having the dented portion and disposing the member having theprotruded portion having one or a plurality of holes in which a hardsolder is inserted so as to closely contact with the layer comprisingthe mixture of at least two fine particle materials differing inwettability with the hard solder; or previously preparing a memberhaving a protruded portion at the end of which is formed a layercomprising a hard solder and a mixture of at least two fine particlematerials differing in wettability with the hard solder, disposing ahard solder on the surface of a dented portion of a member having thedented portion and disposing thereon said member having the protrudedportion having the layer, and a step of heating them to a giventemperature under application of pressure to melt the hard solder andimpregnating the mixture of at least two fine particle materialsdiffering in wettability with the hard solder with said molten hardsolder to form a bonding layer comprising the hard solder and the fineparticle materials, thereby to bond the different members through thefitting structure.
 2. A method according to claim 1, wherein the step ofdisposing the member having the protruded portion comprises uniformlyspreading a mixture of at least two fine particle materials differing inwettability with a hard solder over the surface of the dented portion ofthe member having the dented portion, then disposing a platy or powderyhard solder so as to cover at least a part of the layer comprising themixture of at least two fine particle materials differing in wettabilitywith a hard solder, and further disposing the member having theprotruded portion.
 3. A method according to claim 1, wherein the step ofdisposing the member having the protruded portion comprises uniformlyspreading a mixture of at least two fine particle materials differing inwettability with a hard solder over the surface of the dented portion ofthe member having the dented portion and disposing the member having theprotruded portion having one or a plurality of holes in which a hardsolder is inserted so as to closely contact with the layer comprising amixture of at least two fine particle materials differing in wettabilitywith the hard solder.
 4. A method according to claim 1, wherein the stepof disposing the member having the protruded portion comprisespreviously preparing a member having a protruded portion at the end ofwhich is formed a layer comprising a hard solder and a mixture of atleast two fine particle materials differing in wettability with the hardsolder, disposing a hard solder on the surface of a dented portion of amember having the dented portion and disposing thereon the member havingthe protruded portion having the layer.
 5. A method according to claim1, wherein at least one of the different members is a ceramic member. 6.A method according to claim 1, wherein one of the different members is aceramic member and another is a metal member.
 7. A method according toclaim 1, wherein the fine particles are a fine particle material whichreduces thermal stress.
 8. A method according to claim 2, wherein thefine particles are a fine particle material which reduces thermalstress.
 9. A method according to claim 3, wherein the fine particles area fine particle material which reduces thermal stress.
 10. A methodaccording to claim 4, wherein the fine particles are a fine particlematerial which reduces thermal stress.
 11. A method according to claim1, wherein a base metal of the hard solder is Au, Ag, Cu, Pd, Al or Ni,and the mixture of two or more fine particle materials differing inwettability with the hard solder is a mixture of ceramic fine particles,cermet fine particles or low-expansion metal fine particles which arenot surface treated and ceramic fine particles, cermet fine particles orlow-expansion metal fine particles which are surface treated.
 12. Amethod according to claim 2, wherein a base metal of the hard solder isAu, Ag, Cu, Pd, Al or Ni, and the mixture of two or more fine particlematerials differing in wettability with the hard solder is a mixture ofceramic fine particles, cermet fine particles or low-expansion metalfine particles which are not surface treated and ceramic fine particles,cermet fine particles or low-expansion metal fine particles which aresurface treated.
 13. A method according to claim 3, wherein a base metalof the hard solder is Au, Ag, Cu, Pd, Al or Ni, and the mixture of twoor more fine particle materials differing in wettability with the hardsolder is a mixture of ceramic fine particles, cermet fine particles orlow-expansion metal fine particles which are not surface treated andceramic fine particles, cermet fine particles or low-expansion metalfine particles which are surface treated.
 14. A method according toclaim 4, wherein a base metal of the hard solder is Au, Ag, Cu, Pd, Alor Ni, and the mixture of two or more fine particle materials differingin wettability with the hard solder is a mixture of ceramic fineparticles, cermet fine particles or low-expansion metal fine particleswhich are not surface treated and ceramic fine particles, cermet fineparticles or low-expansion metal fine particles which are surfacetreated.
 15. A method according to claim 11, wherein the ceramic fineparticles, cermet fine particles or low-expansion metal fine particleswhich are surface treated are fine particles covered with a metal byplating or sputtering.
 16. A method according to claim 12, wherein theceramic fine particles, cermet fine particles or low-expansion metalfine particles which are surface treated are fine particles covered witha metal by plating or sputtering.
 17. A method according to claim 13,wherein the ceramic fine particles, cermet fine particles orlow-expansion metal fine particles which are surface treated are fineparticles covered with a metal by plating or sputtering.
 18. A methodaccording to claim 14, wherein the ceramic fine particles, cermet fineparticles or low-expansion metal fine particles which are surfacetreated are fine particles covered with a metal by plating orsputtering.